Myocardial viability and recovery of left ventricular function (LVEF) after revascularization is predicted by the presence of positron emission tomography defined F-18 deoxyglucose (FDG):blood flow mismatch pattern in patients with ischemic cardiomyopathy (ICM). However, little is known about regional blood flow and metabolism patterns in patients with non-ischemic cardiomyopathy (NICM). Therefore, we studied 10 symptomatic patients (NYHA class II and III) with left ventricular dysfunction; 5 had ICM and 5 NICM. All patients underwent radionuclide angiography, stress thallium scintigraphy, coronary angiography and positron emission studies with N-13 ammonia and FDG at rest. The myocardial region with the maximum counts on the stress thallium study was used as the normal reference region for relative ammonia and FDG uptake. From matched ammonia and FDG short-axis images, a total of 156 regions were analyzed in ICM patients and 144 regions in NICM patients. Regional blood flow less than 85% in both thallium and ammonia studies was considered abnormal. FDG:ammonia ratio of equals approximately 1.2 was considered to represent metabolism-blood flow mismatch. abnormal flow mismatch match LVEF (%) ICM 89 (57%) 37 (47%) 52 (53%) 16 +/- 8 NICM 37 (26%) 4 (11%) 33 (89%) 12 +/- 5 *p <0.001 **p <0.005 In ICM patients, 57% of all regions demonstrated abnormal blood flow and almost half of such regions exhibited preserved glucose extraction indicative of ischemic and viable myocardium. In contrast, decreased regional blood flow occurred in approximately one-fourth of NICM regions and the majority (89%) of such regions had matched decrease in glucose extraction (nonischemic). Thus, despite the absence of significant epicardial coronary artery stenosis, decreased regional blood flow occurs in patients with NICM and may reflect regions with admixture of viable myocytes and fibrosis.